古代人类钻木取火，这是利用____的方式改变物体内能的．用热水袋取暖，这是利用____的方式改变物体内能的．

用方框所给出选项完成对话。

Polly: Dad, I want to get a job.

Father : ____ 

Polly: I need money. When I go out with my friends, I never have enough money.

Father: Polly, you know most families here are richer than we are.

Polly: ____  Then, I won't have to ask you for money.

Father: You have a lot of homework everyday. How can you work and study at the same time?

Polly: ____

Father: I have an idea. Once a week, you can come to my shop and help out a bit. You can clean the floors and the windows－that sort of thing. I’ll pay you for each hour you work. How does that sound?

Polly: ____  But I don't want to clean any toilets(卫生间).

Father: ____  It's a deal.

春秋后期，促进了农业上的深耕细作，并为开发山林、扩大耕地创造了条件的是（　　）